Ilanga mesembrine n. sp.

(Figs 27 A–O, Table 18, Key 2: 17)

DNA ref: Ilanga 10 (Williams et al. 2013; Sumner-Rooney et al. 2016)

COI sequence data: GenBank Accession numbers: HF586283, HF586284, HF586285, HF586286, HF586287, HF586288, HF586289, HF586290, LT575891, LT575892, LT575893, LT575894, LT575895, LT575896.

Type material. Holotype (7.0× 12.7 mm) MNHN IM-2009-8805 . Paratypes: 7 MNHN IM-2009-8808, IM-2009- 8806, IM-2009-8807, IM-2009-8797, IM-2009-8799, IM-2009-8798, IM-2009-8800 and 1 NHMUK 20190460 as listed below .

Type locality. South-eastern New Caledonia, TERRASSES, stn CP3087, 22°11’S, 167°12’E, 380–400 m.

Material examined. South-eastern New Caledonia.MUSORSTOM 4: stn DW235, 22°13’S, 167°12’E, 405–415 m, 1 dd (paratype NHMUK 20190460).—TERRASSES: stn DW3079, 22°28’S, 167°29’E, 300–420 m, 1 lv (DNA sample MNHN IM-2009-8809).—Stn CP3087, 22°11’S, 167°12’E, 380–400 m, 6 lv (with holotype MNHN IM- 2009-8805, paratypes MNHN IM-2009-8808, IM-2009-8806, IM-2009-8807).—Stn DW3090, 22°16’S, 167°08’E, 260 m, 1 dd.—Stn CP3092, 22°13’S, 167°12’E, 360–380 m, 4 lv (with paratypes MNHN IM-2009-8797, IM-2009- 8799, IM-2009-8798 & IM-2009-8800).—P. Tirard coll.: 22°40’S– 22°50’S, 167°10’E– 167°30’E, 200–350 m, 3 dd.—EXBODI: stn CP3790, 22°14’S, 167°11’E, 378–414 m, 1 dd.—Stn CP3821, 21°53’S, 166°50’E, 211–440 m, 1 dd.—Stn DW3859, 22°20’S, 169°01’E, 350–388 m, 2 dd.— New Caledonia, Norfolk Ridge. NORFOLK 1: stn CP1716, 23°23’S, 168°02’E, 266–276 m, 1 dd sub.—Stn DW1717, 23°23’S, 168°02’E, 250–312 m, 3 dd, 1 dd sub—NORFOLK2: stn DW2135, 23°02’S, 168°21’E, 295–330 m, 1 lv (DNA sample MNHN 18340).—Loyalty Ridge. MUSORSTOM 6: stn DW421, 20°26’S, 166°40’E, 245 m, 1 dd.—Stn DW423, 20°25’S, 166°40’E, 263–290 m, 1 lv.—Stn DW479, 21°09’S, 167°55’E, 260–360 m, 1 dd.—Stn DW481, 21°22’S, 167°50’E, 300 m, 1 lv.—Northern New Caledonia. EXBODI: stn DW3928, 18°38’S, 164°20’E, 362–402 m, 1 dd, 1 juv sub.— New Caledonia, Bellona. EBISCO: stn DW2547, 21°06’S, 158°36’E, 356–438 m, 2 dd.

Distribution. New Caledonia area, 245–405 m, lv at 290– 380 m.

Diagnosis. A rather large, lenticular Ilanga species with a depressed spire, a subangulate periphery with some faint spiral cords, 5 spiral cords on first teleoconch whorl, no subsutural pleats, very broad angulate umbilicus with a spiral cord at rim, without or with weak axial pleats around the umbilicus (especially near the aperture), 2 to 8 smooth thin spiral cords inside.

Description. Shell: Rather tall for genus (H up to 7.2 mm, W up to 13.4 mm), much wider than high, lenticular, glossy; spire depressed, height 0.50×to 0.55×width, about 1.54×to 1.91×aperture height; periphery subangulate; umbilicus very broad and deep. Protoconch ca. 380 μm wide, 1.25 whorls, rounded, with 3 thin, evenly spaced, spiral cords and with a straight, slightly expanded terminal lip. Teleoconch up to 4.8 convex whorls with a weak subsutural ramp on first whorls but vanishing on last whorls; early teleoconch whorls with 4–5 smooth spiral cords, quickly vanishing; last whorls smooth with poorly visible spiral threads near periphery. Suture weakly canaliculated on first whorl, impressed on later whorls. On first teleoconch whorl, 5 spiral cords appearing immediately; P2 strongest, at edge of subangulate subsutural ramp; thin axial threads between cords; P3 and P4 vanishing at end of whorl, P5 disappearing on next whorl. On second whorl, P1 vanishing near end of whorl; P2 very weak, but still present; subsutural ramp weakening; narrow translucent subsutural spiral band appearing. On third whorl, subsutural ramp vanishing; axial threads no longer visible. Last whorls smooth, with some faint spiral cords situated around periphery. Aperture rounded triangular; peristome incomplete; outer and inner lip thin; inner lip without obvious thickening against umbilical rim. Base convex, smooth, usually without or only with weak (especially near aperture) axial pleats around umbilicus; thin spiral cord bordering umbilical rim. Umbilicus broad (diameter 30–35% of shell width), central, with perspective to apex, with angulate rim, with vertical to slightly concave wall; 2 to 8 smooth thin spiral cords on umbilical wall, usually gathered in adapical part, without axial threads; axial pleats on umbilical walls of adapical whorls.

Colour: Teleoconch nacreous white, with 3 bands: adapical one brownish orange chevron patterned, median one with brownish patches and abapical one also brownish orange chevron patterned; base paler with regular brownish patches on external half.

Operculum: Corneous, multispiral with central nucleus, light brown.

Remarks. Ilanga mesembrine n. sp. weakly resembles I. gotoi (Poppe, Tagaro & Dekker, 2006) (Figs 10 A–H) from the Philippines, but I. gotoi is larger (H up to 8.5 mm, W up to up 18.4 mm), has 4 Pi, a much stronger spiral cord around the umbilicus and more spiral cords inside the umbilicus (18–20, instead of 2–8 in I. mesembrine n. sp.)

Etymology. From the South (Ancient Greek: μεσημϐρινός, ή, όν)—after the type locality in south-eastern New Caledonia.